1. Field of the Invention
This invention relates to a rotationally symmetrical star-shaped driving feature, preferably for rotatable fasteners, such as, e.g. screws, and the associated drive tools.
2. Description of the Related
Driving features of this kind, also referred to as drive systems, are known in the prior art.
These are designed either as external driving features or as internal driving features and for the purposes of this application the terms “external driving feature” or “external drive” and “internal driving feature” or “internal drive” always refer to the type of driving feature on the fastener, i.e. on the screw. An external driving feature can therefore be driven by a tool having a corresponding internal driving feature and vice versa.
The oldest driving feature of this kind is the common hexagon drive, already known for centuries as an external driving feature and marketed by the Applicant as an internal driving feature, e.g. under the trade mark “INBUS®”.
The Applicant has also provided corresponding developments in this area, namely the hexalobular driving features available on the market under the trade mark “Torx®”, as well as the further improved flattened hexalobular driving features sold under the trade mark “Torx Plus®”.
These hexalobular driving features offer many advantages over conventional drives such as the hexagon drive, such as high force transmission, long tool life and the option of a low-profile design, i.e. a particularly flat design for the driving features in order to save weight.
However, problems are frequently encountered with these modern driving features during maintenance and repair work, as the corresponding special tools suitable for the respective driving features are not available in every required size in every workshop.
When a fastener such as a modern hexalobular driving feature has to be removed during repair work, there has hitherto been no alternative other than to use the drive provided especially therefor.
Some sections of the German automotive industry have already recognised this problem and have therefore been quite restrained in their use of modern hexalobular driving features, particularly the “Torx Plus®” drive, as corresponding tools for this drive system are not available in Europe or can only be obtained with extreme difficulty. The situation would appear to be similar in the burgeoning Asian market.
Furthermore, in the known driving features, forces are transmitted between the tool and the fastener via very small, sometimes only linear pressing surfaces, resulting in high surface loading.
In addition, the normal force produced at the contact point, i.e. the force acting perpendicularly to the contact surface, passes through the outwardly projecting corner, e.g. of a hexagon screw and therefore acts upon this corner as an undesirable shear force, which may lead to premature failure of this drive.